The present invention relates to a method for adapting the adjustment of a clutch in an unconventional drive train of a vehicle.
Automatic clutches are increasingly used not only due to the enhanced comfort they provide but also because of the possible fuel economy in motor vehicles.
FIG. 5 shows an exemplary block diagram of a drive train of a motor vehicle equipped with an automated clutch. The drive train contains an internal combustion engine 2, a clutch 4, and a transmission 6, which is connected to the driving wheels via a drive shaft 8. Transmission 6 is an automated manual transmission, for example, or a V pulley transmission having a continuously variable reduction ratio. An actuating device 9, which is controllable in a known manner by a selector device 10 having a selector lever 12 via a control unit 14, is used for actuating or shifting transmission 6. Of course, the selector device may also have a different design, for example, as a conventional shift stick or a lever with up- and downshift positions. Clutch 4 is, for example, a friction disk clutch of an essentially known design, having an actuating device 16, which may be of a hydraulic, electrical, electrohydraulic, or other known design.
The sensors contained in the drive train such as a pressure sensor 18 for detecting the intake pressure of engine 2, a rotational speed sensor 20 for detecting rotational speed nM of the engine crankshaft, a sensor 22 for detecting position a of an accelerator pedal 24, a sensor 26 for detecting the position of selector lever 12, and another rotational speed sensor 28 for detecting the speed of drive shaft 2 are connected to the inputs of control unit 14.
Characteristic maps and programs for controlling actuators such as a load adjusting element 30 for adjusting the load on engine 2, actuating device 16 of clutch 4, and shifting device 9 of transmission 6, as well as other consumers 31 directly or indirectly driven by the engine such as a generator, a pump, or a heating element, etc. are stored in control unit 14, which contains a microprocessor and respective memories 29 in a known manner. The individual actuators may be designed in such a way that their positions are directly communicated to control unit 14, for example, as stepping motors, or other position sensors such as position sensor 32 for detecting a parameter that is relevant to position sK of the clutch, may be provided.
Another control unit 34, which controls vehicle brakes 35, for example, as known from antilock systems or driving stability systems, is connected to control unit 14 via data bus 33. The hardware and software distribution between units 14 and 34 is adapted to the particular conditions.
The design and function of the above-described device are essentially known and are therefore not explained here in detail. Load adjusting element 30, actuating device 16, and shifting device 9 are actuated in a mutually synchronized manner according to a driving intent communicated via accelerator pedal 24 and the driving program request communicated via selector lever 12 as a function of the signals delivered by the sensors, so that smooth and/or fuel-saving driving results.
A characteristic curve, which determines, as a function of the torque to be transmitted by clutch 4, a setpoint position of clutch 4, set by actuating device 16 for actuating clutch 4, is stored in a memory of control unit 14, for example. For reasons of control quality, clutch wear, and power consumption by actuating device, the clutch torque to be transmitted should not exceed the absolutely necessary value. The necessary torque to be transmitted is obtained from the driver's intent, i.e., the position of accelerator pedal 24 and, for example, from the load on engine 2 detected by sensor 18, as well as additional operating parameters such as the speed of engine 2, etc.
The characteristic curve stored in control unit 14, which provides the setpoint path of an adjusting element moved by actuating device 16 as a function of the calculated torque to be transmitted has a decisive influence on a smooth start and a smooth shifting process. The characteristic curve changes short-term, for example, due to temperature changes, and long-term over the lifetime of the clutch due to wear, for example. Therefore it is continuously updated, i.e., adjusted according to different strategies in the presence of certain operating conditions.
FIG. 6 shows in detail an example of an actuating device 16 having a hydraulic connector.
A piston 38, whose shaft 40 has external teeth meshing with the internal teeth of a gear 41, which in turn engages with the external teeth of a pinion 42 of a small electric motor which is activated by control unit 14 (FIG. 5), moves in a sensor cylinder 36 filled with hydraulic fluid. The motor may be of any suitable design and is activated using a PWM (pulse width modulation) signal, for example. The motor is advantageously a stepping motor. Transducer cylinder 36 has vent hole 44, which is connected to an equalizing container via a line 45. A line 48 connects pressure chamber 46 of the cylinder to a slave cylinder 50, in which a piston 52 moves, which is connected, by its shaft, to a disengaging lever 54 of the clutch, forming an adjusting element, for example. Position A, which is referred to in general as a venting position, is the position which, when piston 38 passes beyond vent hole 44 in FIG. 6 to the right and pressure is built up in pressure chamber 46 for actuating (i.e. opening) the clutch.
An incremental position sensor 32, for example, of a known design, which counts the teeth of gear 41 moving past it and delivers the corresponding pulses to control unit 14, is provided for position sensing. The number of these pulses is a direct measure of the displacement of sensor piston 38 and, when sensor piston 38, as shown in FIG. 6, is to the right of venting position A, of movement of disengaging lever 54.
In a venting sequence, sensor piston 38, preferably having a check valve integrated in it, which opens in the event of overpressure on the left side of piston 38, moves to the left beyond venting position A, in such a way that the hydraulic link between pistons 38 and 52 is connected to line 45 and is depressurized. In this depressurized state of the hydraulic link, disengaging lever 54 assumes its fully closed position, i.e. the engaged position of the clutch. If sensor cylinder 38 is then moved by motor 42 to the right, disengaging lever 54 is actuated at the time when sensor piston 38 moves over venting position A. This position of sensor piston 38 may be detected in various ways, the count of position sensor 32 being stored in control unit 14 as the closed position.
In addition to the closed position of the clutch, it is important to know the gripping or contact point of the clutch, also known as the biting point, i.e., the position in which the clutch transmits a predefined small torque, of 4 Nm for example. Knowing the gripping point exactly is important because it plays an important role in start and shifting. When the clutch disengages beyond the gripping point, it is completely disengaged. If the clutch is not actuated up to the gripping point, gear shifting is impossible without considerable impairment in comfort or even risk of damage to the transmission, and the vehicle creeps considerably.
The gripping or contact point is normally set by disengaging the clutch completely in certain operating states of the drive train, for example, with the vehicle stopped, the brake actuated and transmission in gear, and then engaging it slowly, while the engine torque is measured. If the engine torque, which is easily obtained in an engine equipped with idling regulation, for example, via an adjusting element of the idling regulator, reaches the predefined value while the clutch is being slowly engaged, position sensor 32 is read and its value is stored as the gripping point of the clutch. The gripping point may thus be quickly reached and used as the orientation value for performing a start sequence or a shifting sequence. A gripping or contact point adaptation takes approximately five seconds and is typically performed once per trip.
Similarly, individual points of the path/torque characteristic curve of the clutch, stored in the control unit, may be updated or adapted by determining the clutch torque, reading the corresponding position of the actuating device or position sensor 32, and storing it as the updated or adapted new position. The clutch will slip when engaged at a relatively high clutch torque, the clutch torque being determined by determining the torque of the engine, taking into consideration its speed change and moment of inertia. The clutch characteristic curve, which changes due to changes in the coefficient of friction of the clutch, may then be adapted in this way.
In venting, the sensor cylinder briefly returns to its venting position as explained above. The clutch is completely engaged. A venting sequence takes approximately 400 ms and may take place with an interval of a few minutes.